The present invention is related to switching light signals or optical signals using planar optical components and more particularly to equipment and methods which provide high speed switching of light signals in fiber optic networks and communication systems by inducing internal reflection at a junction between two waveguides.
The increased demand for data communication and the remarkable growth of the internet have resulted in increased demand for communication capability within metropolitan areas. There has also been an equally large increase in demand for communication capability between large metropolitan areas. Optical communication systems using a network of fiber optic cables are being developed and installed to meet this increased demand.
Various types of optical switches and techniques are currently used in communication systems and computer systems. Many currently available optical switches are based upon optoelectric and electrooptic conversion of light signals and electrical signals within the associated optical switch. One type of presently available optical switch includes a matrix of thermooptic switching elements interconnected by waveguides formed on a silica substrate. Switching of light signals is accomplished by the use of thin film heaters to vary the temperature of the switching elements. Electrical circuits are also provided to supply switching current to the heaters. A heat sink may be provided to dissipate heat caused by the switching operations. One example of such switches is shown in U.S. Pat. No. 5,653,008.
Various types of planar optical switches are currently available for some applications. Such planar switches are often fabricated by Ti-difusion in LiNbO3. Switched directional couplers represent one example of LiNbO3 based switches which are commercially available. This type of planar switch functions very rapidly in the sub-nanosecond range. However, LiNbO3 based switches are generally polarization sensitive and relatively expensive.
For some switching applications, polarization insensitivity is more important than high speed switching of light signals flowing through a switch. Polarization insensitivity is particularly important for bypass switching in local area networks (LAN) and some wide area networks (WAN). Also, polarization insensitivity is a particularly desirable characteristic for circuit switching during distribution of video and graphic information. Optical waveguide switches using polarization independent thermal optic effects have been satisfactorily used when polarization insensitivity is required. However, such optical waveguide switches often have switching times in the range of milliseconds.
Some presently available optical switches include a semiconductor substrate with vertical current flow to heat active regions of an associated optical switch. One example of such switches is shown in U.S. Pat. No. 5,173,956. Some optical switches require mode perturbation to generate required mode patterns for the desired switching function. Examples of such optical switches include directional couplers and Mach Zhender interferometers. Such optical switch designs often have poor scalability, relatively high manufacturing costs and low optical signal bandwidth.
In accordance with teachings of the present invention, an optical switch is provided which substantially reduces or eliminates disadvantages and problems associated with presently available optical switches. The present invention provides an optical switch which uses internal reflection at a junction formed by two waveguides intersecting with each other at a selected angle. For some applications, substantially total internal reflection (TIR) will occur at the junction between the two waveguides in response to heating from a thin film electrode. For other applications, the desired internal reflection may be produced by electrooptic, magnetooptic or acoustooptic effects. The use of TIR in accordance with the teaching of the present invention may be used to provide a wide band optical switch which is not wavelength dependent.
An optical switch formed in accordance of teaching of the present invention provides a very high data-rate via an independent path for communicating optical signals between terminals once the optical switch has made the desired connection. Technical advantages of the present invention include a low cost, reliable optical switching device that may be integrated into a miniaturized version with system interchangeability in optical networking systems. An optical switch incorporating teachings of the present invention is intrinsically a wide band device covering all S-band, C-band and L-band optical signals.
The optical switch may be fabricated on a wide variety of materials such as polymer/SiO2, polymer/polymer, polymer/polymer/polymer and semi-insulating/semiconductor substrates. The optical switch may be used in general purpose optical communication systems including fiber optic networks associated with modern metropolitan communication systems.
One aspect of the present invention includes a thermal optical switch having a two channel waveguide array with inputs and outputs well matched for use with single mode fibers. A junction formed by intersection of the waveguides with each other is relatively small to maintain substantially no cross talk between the respective waveguides while maintaining a relatively large dynamic range of low-cross talk and therefore, a small insertion loss. Beam propagation methods (BPM) may be used to determine characteristics of the junction such as dynamic range. An electrode may be placed on top of the intersection or junction of the waveguides along with both an electrical current input port and a grounding port located at the surface of the respective waveguides. Current may be introduced from the input port to flow through the electrode to the grounding port which creates sufficient heat to modulate the index of refraction within a portion of the waveguides disposed beneath the electrode. As a result of heat created by the electrode, the index of refraction will be reduced. The portion of the junction or intersection disposed underneath the electrode may encounter total internal reflection effect which provides desired switching of optical signals from one waveguide to the other waveguide. The location of the electrode may be selected in accordance with teachings of the present invention to maximize switching efficiency through temperature induced perturbation.
Two dimensional arrays formed in accordance with teachings of the present invention may be satisfactorily integrated to form a wide variety of arrays such as two by two, eight by eight, sixteen by sixteen and sixty-four by sixty-four. The resulting arrays may be hermetically sealed using appropriate semiconductor fabrication techniques. An optical switch formed in accordance with teachings of the present invention may be satisfactorily used in optical communication systems including fiber optic networks having cable lengths ranging from one hundred meters to thousands of kilometers.
Typical specifications for an optical switching device formed in accordance with teachings of the present invention include cross talk between adjacent waveguides of less than thirty (30) dB, insertion loss of less than five (5) dB per waveguide for an 8xc3x978 switch, polarization independent return loss greater than forty (40) dB and a relatively fast switching time for a thermal optic device. For various applications the switching time may range from less than twenty milliseconds to much less than a millisecond.
Technical benefits of the present invention include providing an optical switch which does not require conversion between optical signals and electrical signals.